Angle joints of the general type described above are known from a variety of publications. For example, in the German Auslegeschrift No. 1 525 177, there is described an angle joint in which the locking element is a bow spring which is pivotably attached to one end of one of the jaws of the ball socket. After the ball has been emplaced in the ball socket, the bow spring is pushed over a protrusion at the end of the other jaw, thereby rigidly locking together the two ends of the jaws. An improvement of the aforementioned swivel joint is described in the German Auslegeschrift No. 1 625 581 where the bow spring is attached to one jaw of the plastic ball socket by means of a flexible strip hinge and the bow spring has an internally bent extension which engages a suitable nose at the other jaw. A strip-like hinge of this type is easily damaged and an improvement according to the German Auslegeschrift No. 19 21 769 thus proposes attachment of the bow spring which serves as a closure element to one of the jaws of the ball socket while a slot in a protruding leg of the jaw provides elastic locking of the two jaws. This basically very attractive solution has the disadvantage that relative motion between the two jaws of the ball socket is possible, thus failing to insure the reliable seating of the ball within the ball socket.
Another angle joint is described in the German Offenlegungsschrift No. 25 12 253 which deals with a ball and socket joint wherein the ball socket has an elastically yielding part which moves out of the way when the ball of the ball pin is pushed into the ball socket and which is then locked into place by driving a bolt into a suitable recess. This construction is also very attractive but has the disadvantage that the ball belonging to the ball pin is seated only over part of its surface and that, furthermore, the complication of the construction of the ball socket presents great problems from the point of view of manufacture in plastic injection molding technology.
The British Pat. No. 838,095 describes an angle joint in which the ball socket is divided by a slot which extends over only a portion of the ball socket and not fully to an extremum thereof. After the ball has been emplaced, a bow spring is pushed into place. One disadvantage of this construction is that the insertion of the ball pin is difficult and requires a great deal of force because the relatively short slot permits only a limited spreading of the ball seat. Another disadvantage is that the bow spring which is pushed over the ball socket does not provide reliable insurance against unintentional disengagement of the ball.
The German Pat. No. 660 303 describes an angle joint having a ball socket which is split by a slot extending up to the free end of the socket and which divides the socket into two elastically enlargeable jaws. After the ball has been seated, a cap is pushed over the ends of the jaw and locked into place by means of a key or a bayonet closure. The emplacement of the closure cap in this construction is very difficult.
Other angle joints are described by the German Industrial Normalization Document (DIN) No. 71802. These angle joints have the disadvantage of gradual wear, requiring periodic replacement. Furthermore, the spring lock described in this publication is relatively expensive.